The story behind the periodic table – and the crucial role played by women
Written by Jenny Sharwood, OAM
MACE, FAIE, FRACI-CChem,
Chair, RACI (Vic) Chemical Education Committee
Published 15 June 2020
In 2019 chemists around the world celebrated both the 150th anniversary of the establishment of the modern periodic table and the centenary of the founding of the International Union of Pure and Applied Chemistry (IUPAC), which was established in 1919 as successor to the International Congress of Applied Chemistry. Its members are national chemistry societies, national academies of science, and other bodies representing chemists. Its decisions are made through intensive discussions and debates by chemists who are members of its relevant international committees.
To really appreciate the periodic table, however, we need to go back to where it all started.
The real story of the periodic table is a very human one – and a very long one – dotted with some very interesting tales, some delightful, some showing big leaps in thinking, and others showing how egos and rivalries and prejudices can get in the way.
It took many incredible inventions, lives dedicated to research, and international collaboration between many chemists and physicists before we could arrive at where we are now.
I would like to give you just a taste of some of these stories.
First, it is well to appreciate the fact that all the elements on Earth were created in nuclear reactions in stars billions of years ago. These were much bigger stars than the Sun, and much, much older.
As our developing Earth hurtled through space as a molten ball and even when it started to cool and settle into layers, the atoms of all the different elements it contained kept colliding with each other and as a result, most of them reacted with one another and kept on reacting . . . what a seething mass of chemicals it must have been!
As a result of all this turmoil, by the time the early civilisations sprang up, most elements could only be found in Nature in compound form, buried within mixtures of many compounds.
No matter which of the early civilisations you might think of – including those in Egypt, Afghanistan, China, India and Tibet – people mined and processed many of these natural resources to produce things they needed and things they desired: weapons, tools that included mortars and pestles, containers, food preservatives, jewellery, dyes for fabrics, cosmetics and perfumes. This involved a lot of experimentation.
According to the fascinating book, Hypatia’s Heritage, it was mostly the women who were at the forefront of all this experimentation and processing, while the men were more occupied with hunting and building. In addition, it was mainly women who were their physicians and surgeons and who discovered the medicinal properties of various plants, oils, minerals and metals.
So it was the women, first and foremost, who were the world’s first chemists! They invented and built equipment, and they discovered how to extract, break down, separate and purify substances.
Women are also said to have played a prime role in the founding of alchemy, the earliest form of chemistry. It is likely this began when it was observed that fire could transform substances into new substances.
But let us overturn some popular misconceptions about alchemy and its practioners, known as the alchemists. Alchemy was both a science and a philosophy of life. True alchemists did not want to conquer Nature or to merely to observe it. They wanted to work in partnership with Nature to help it improve.
Alchemists believed that the perfect material was gold, because it shone like the Sun, which they viewed as the giver of life. One of their aims, therefore, was to transform other materials into gold, which they thought could be achieved by speeding up the transformations of minerals and metals that occurred naturally but very slowly.
Some thought that a magical substance would enable them to do this – it was generally known as ‘the philosopher’s stone’, though in India it was called ‘the jewel of the wise’.
They also believed that they should only perform their experiments with a pure heart. So they must not only transform natural objects to greater perfection, but also their inner selves. So they restricted their work to sacred places, underwent cleansing rituals so they were morally worthy, and recorded their findings in symbols and metaphors so their knowledge did not fall into the wrong hands.
Unfortunately it was the actions of unscrupulous people who posed as alchemists in order to cheat people that led to them being misjudged and even persecuted.
But the truth is, it was the alchemists who discovered much of our valuable chemical and medical knowledge, and developed many of our widely used laboratory techniques!
One of the greatest times for the alchemists arose when the Greek warrior Alexander the Great, having conquered Egypt in about 332 BCE, established the city of Alexandria. This became a truly multicultural city, in which women were equally valued with men, and which boasted a great library, an observatory, dissecting rooms and botanical gardens.
Scholars came there from all over the world. With the introduction of Greek philosophy, including the proposal that all matter was made from earth, air, fire and water, the alchemists of Alexandria were possibly the first scientists to combine theory with experiment.
One name that stands out from this time of great enlightenment was that of Maria the Jewess, who in about the 1st century CE invented water baths and sophisticated distillation apparatus, which was very like the apparatus used today. One of her inventions is still in use today, not only in chemistry laboratories but also even in some restaurants. This is the bain-marie, a French term that literally means ‘Maria’s bath’.
Tragically, two centuries later, the Roman Emperor Diocletian attacked Alexandria and burned down the entire library. All the records held there of the incredible knowledge of chemistry, medicine, mathematics, astronomy, and so on, that had been built up in those great civilisations were destroyed in one blow! What a tragic loss!
Another great blow to women in chemistry in those early years was the assertion of the famous Greek philosopher Aristotle that females are merely ‘deformed’ males. This was published in his very influential work on embryology, De Generatione Animalium, which publication was based on what he observed when he dissected hundreds of animal species.
To quote from Hypatia’s Heritage
“This bias against women was incorporated into most systems of natural philosophy and contributed to the widespread belief, amongst both men and women, that science was the domain of the male!”
In addition, Aristotle firmly believed that all matter is made up of the four elements earth, air, fire and water and vehemently opposed the theory proposed around 500 BCE by the Greek philosophers Leucippus, and later by his student Democritus, that matter is made of atoms.
Unfortunately, when these theories of Aristotle were brought to Europe in about the 12th and 13th centuries, they were embraced by the churches as having an almost divine authority. Those who opposed them were prosecuted. As late as 1624, the Parliament of Paris passed a law compelling all chemists to teach Aristotle’s four-element theory on pain of death or confiscation of goods! This was the Dark Ages for western chemistry.
Despite all that at least one French alchemist, Marie Meudrac, buried herself in her research work. In 1666, she published her first report on all her discoveries. She described laboratory apparatus she had invented and laboratory techniques she had developed. Her report displayed tables of atomic weights of various substances, the results of her experiments on metals and instructions on how to prepare a number of medicines and cosmetics.
In contrast to this, the discovery of phosphorus three years after Marie published her findings, showed a very different kind of character involved in alchemy, one who undermined its reputation and hence was not a true alchemist. This was the German ‘alchemist’ Hennig Brandt, who had believed that since urine was golden, it may contain the philosopher’s stone. He boiled a large sample of urine to a dry residue and kept on heating it, until his retort glowed red hot. Suddenly the vessel was filled with glowing fumes and a shiny liquid dripped out that burst into flames. He trapped this liquid in another vessel and discovered that when it solidified a green glow and flames emanated from its surface. He had discovered phosphorus!
Instead of publishing his discovery, however, he kept it secret for several years, hoping to become very wealthy from it. After a few years, when he still had not managed to isolate the philosopher’s stone, he told a few people about this glowing new material but not about how he made it or what its origin was. But others guessed what he did and eventually made the same discovery. In the end Brandt had made no money out of it and faded into obscurity. Interestingly, all his research was financed using the wealth of his two successive wives.
Back to a more ethical practitioner . . .
Around that time, the Irish chemist Robert Boyle vainly attempted to isolate Aristotle’s four elements and in his book The Sceptical Chymist, he questioned the validity of the theory and emphasised the importance of conducting accurate experiments to test hypotheses.
Fortunately, thanks to Boyle’s influence, there was an increased questioning of the assumptions behind the theories of Aristotle and others. It was realised that theories must be backed by experimental evidence. This was the start of the age of enlightenment and the adoption of the ‘scientific method’. So the late 17th century became a time when chemistry knowledge started to develop very rapidly. New instruments such as accurate weighing scales and thermometers were invented.
Many highly respected scientists such as Sir Isaac Newton also practised alchemy around that time.
In 1730 he declared his support for the atomic theory suggested by Leucippus, but proposed atoms are held together by mutual attraction, not by the little hooks that the Greek philosopher had envisaged.
After oxygen was discovered in 1774 and hydrogen in 1781, quantitative experiments on the combustion of hydrogen that were conducted by both Antoine and Marie Lavoisier led them to conclude the four-element theory cannot be correct. They also were able to explain what combustion actually involved.
It is important to remember that Marie played an integral part in all of Antoine’s research work after marrying him at the age of 14. Clearly very gifted, she also translated their reports into other languages and did all their technical drawings.
After conducting some brilliantly designed experiments, the Lavoisiers wrote the first modern chemistry textbook: Elements of Chemistry, which was published in 1789. In the book it was proposed that an element is a substance that cannot be decomposed by any method. The 23 elements known at the time were listed in the book.
Little were they to know that the discovery in Italy in 1781 that a dead frog’s leg could be made to kick, would lead to the discovery of a new way of breaking down substances and the consequent discovery of new elements just 20 years later!
But Antoine was to never know that – tragically he died at the age of 50, just five years after publishing the book, another victim of the excesses of the French revolution. What an enormous loss to chemistry!
It all began when the Italian medical scientist and anatomist Luigi Galvani removed the legs and lower spine of a recently killed frog and touched the nerves of the lower spine with a clean copper wire and the muscles with a zinc wire. When the two metals were brought into contact, electricity was detected and the legs twitched. This led to all kinds of fascinating hypotheses and experiments about the nature of electricity and the production of electrical currents in the body. His first report was published in 1791, just two years after the Lavoisiers published their book.
Unfortunately, Galvani was then subjected to certain political machinations by the local republican governors, who stripped him of his professorship because he would not take a civic oath they demanded of him. His theories were attacked and repudiated and on top of that, his beloved wife died. He ended up dying in poverty in a state of profound melancholy just a few years later. But his nephew, Professor Aldini of Bologna, was appalled by the way he had been treated and in an effort to restore his uncle’s reputation, took his work to France and England, where it greatly interested a number of scientists.
Up until then, scientists only knew how to generate static electricity. Galvani’s discoveries led to invention of all kinds of interesting batteries that could generate current electricity. One of these inventions was Volta’s pile, developed by the Italian physics professor and chemist, Alessandro Volta, who is often credited with being the inventor of the modern battery.
The pile consisted of a tower of 40 pairs of alternating silver coins and circular pieces of zinc separated by cloths soaked in salt solution. When wires attached to the two ends were touched together, the person holding them got a big shock. Volta apparently loved tricking his friends into being shocked.
Others improved on Volta’s inventions, and so finally the stage was set for the experiments that were conducted by the English scientist Humphrey Davy early the next century. Hitherto highly stable mineral salts that seemed impossible to break down any further, finally were split up by passing an electric current through the molten salt.
The first element Humphrey discovered was potassium in 1807. He apparently was so excited at seeing these tiny silver-coloured globules rise to the top of the molten liquid then burst into a purple flame, his lab assistant recorded that he danced around the room! That would have been fun to watch!
The next year, according to Cyclopaedic Science, by Professor J H Pepper, which was published not long after the Great London Exhibition of 1850, Humphrey managed to discover Na, Ca, Sr, Mg, Ba and Al!
Apart from being very exciting discoveries, this was the first time chemists could start to question the assertion made by many that elements are unique and unrelated. Here were some elements that had many common properties! For example, K and Na both reacted quite violently with water.
Later Mendeleev was to say that Humphrey Davy’s experiments were some of the most important discoveries ever made.
The stage was now set for the discovery of patterns in the properties of elements when arranged in order according to their atomic weight.
The earliest publication on these patterns appears to have been written by the German chemistry professor Johann Dobereiner in 1829.
He reported that there were groups of three elements, which he called triads, which were related to one another. When arranged in order of increasing atomic weight, the one in the middle had both an atomic weight and properties about halfway between those of the other two.
Two examples of these triads were Ca, Sr, Ba and Li, Na, K.
The test of a theory is that accurate predictions can be made from it. From this Dobereiner predicted there was an element that would have an atomic weight halfway between that of chlorine and iodine, and properties in-between theirs. A few years later, the prediction came true when bromine was discovered.
Unfortunately little notice was taken of this work.
In 1860, however, a very significant event occurred. It was the very first international conference of chemists, which was held in Germany. Participants shared their experimental discoveries, and definitions of elements, compounds and atomic weights were agreed upon. This was the catalyst for even more research.
Two years later a French geology professor, Alexandre de Chancourtis, published a cylindrical arrangement of the 24 elements known at the time, which he called a ‘telluric screw’, so-named because the element tellurium was located at the midpoint of the helix.
The lines along the rows that sloped upwards at 45 degrees, read (starting at the bottom and winding upwards with increasing atomic weights):
H, Li, Be, B, C, N, O, … F, Na, Mg, Al, Si, P, S, … Cl .. K, Ca
As a result of this line-up, elements that had a difference in their atomic weight of 16 ended up in the same vertical line. So F and Cl were in the same line. Li, Na and K were in the same line, and so on. You can see how much this was on the right track!
So de Chancourtis wrote a paper arguing that the close similarity between elements in the same vertical line suggested that the properties of elements occur in repeating patterns and are related to their atomic weights. He presented his paper and a model of his telluric screw to the French Academy.
This was possibly the first time the periodic law was discovered and announced!
But like Dobereiner’s triads, it received little attention. In his case it was because his publisher failed to include an image of the helix in his paper and also made other problems for him.
What both Dobereiner and de Chancourtis also had to deal with was prejudice and obstinacy. Most chemists were stuck in their view that the elements were unrelated.
The same problems occurred in England. At the same time as de Chancourtis was working on his paper, the English chemist John Newlands was also trying to discover patterns in the properties of elements. He listed the known elements in order of increasing atomic weight and gave each element a number. He noticed that every 8th element had simular properties, which he called the ‘Law of Octaves’.
At that stage, the noble gases had not been discovered, or of course it would have been every 9th element . . .
Newlands designed a table in which elements were listed in order of their increasing atomic weight. Elements with similar properties were placed in the same column. When more elements were discovered, he modified the table to include them.
Sadly, when Newlands submitted his paper to the Royal Society in 1864, at the age of 27, his work was ridiculed.
Can you imagine all those old men sitting around him in their round theatre, pointing at him and mocking him? I wonder how much of that was driven by jealousy, seeing a fresh young mind taking a giant leap in thinking. On top of that, no doubt because of their reaction, the editor of the Royal Society’s journal refused to publish his paper.
Five years later the famous table designed by the Russian chemistry professor Dmitri Mendeleev was published and hailed as a landmark discovery. It was not greatly different from Newlands’ table.
It was 18 years after that again before the Royal Society finally acknowledged that Newlands has made one of the most important contributions to the Periodic Law and awarded him the Davy medal. But it was too late. Like his French counterpart, having been treated like that, he just buried himself in lesser work for the rest of his life.
Back to the story . . . Two of the participants in that international chemistry conference were Mendeleev and the German chemist Julius Lothar Meyer. In 1860 they each went on to independently formulate their own version of the periodic table.
Meyer meticulously recorded and graphed physical properties such as atomic volume, volatility, malleability and electrochemical behaviour against atomic weight and observed repeating patterns.
Mendeleev, on the other hand, had collected data on the chemical properties of the known elements for over 20 years. It is doubtful he was even aware of Newlands work, but like Newlands, he set up a table in which elements with similar properties were placed in the same vertical columns. But one reason why he was more successful is that he left some gaps and predicted the atomic weights and detailed properties of as yet undiscovered elements that would fit into these gaps. When three of these missing elements were discovered and behaved as he predicted, his table was accepted.
Of course now we know why there are patterns in the properties of the elements and that is because there are patterns in the electronic configurations of their atoms. But the discovery of that is a whole other story.
So is it any wonder that many think the periodic table of the chemical elements is a very exciting, amazing thing? It is far, far more than just a list.
Said the philosopher CP Snow, on seeing the periodic table for the first time:
“For the first time I saw a medley of haphazard facts fall into line and order. All the jumbles and recipes and hotchpotch of the inorganic chemistry of my boyhood seemed to fit themselves into the scheme before my eyes – as though one were standing beside a jungle and it suddenly transformed itself into a Dutch garden.”
Some recommended reading
Hypatia’s Heritage, Margaret Alic, The Women’s Press, 1986.
Uncle Tungsten, Oliver Sacks, Picador, 2001
The Shocking Story of Phosphorus. A Biography of the Devil’s Element, John Emsley, PAN books, 2000
The Chemical Choir. A History of Alchemy, P G Maxwell-Stuart, Continuum, 2008
Seven Elements that Changed the World, John Browne, Pegasus books, 2014
The Periodic Table, Primo Levi, 1975, published in English 1984, Everyman’s Library